Method and apparatus for making a string of molded electrical resistors



June 28, 1966 w. J. FERNAN ET AL METHOD AND APPARATUS FOR MAKING ASTRING OF MOLDED ELECTRICAL RESISTORS 6 Sheets-Sheet 1 Filed 001.. 9,1962 ATTOQ/VEYS.

June 28, 1966 w. J. FERNAN ET AL 3,257,709

METHOD AND APPARATUS FOR MAKING A STRING 0F MOLDED ELECTRICAL RESISTOR-SFiled Oct. 9, 1962 6 Sheets-Sheet 5 5g \o 41 /23 P15. 4

/4 INVENTORS 5 2 I9 WILL/AM J. FER/VAN W/LL 64M J. HEPBST BY 521.5 I.SHOBEQT 11 ATTUR/VfVJ June 28, 1966 w. J. FERNAN ET AL 3,257,709

METHOD AND APPARATUS FOR MAKING A STRING OF MOLDED ELECTRICAL RESISTORSFiled Oct 9, 1962 6 Sheets-Sheet 5 INVENTORS W/lL/AM J. FElQ/VANIV/LL/JM J. 195E857 BY 245 1'. SHOBEQT 11' ATTORNEYS.

June 28, 1966 w. J. FERNAN ET AL 3,257,709

METHOD AND APPARATUS FOR MAKING A STRING OF MOLDED ELECTRICAL RESISTORSFiled Oct 9, 1962 6 Sheets-Sheet 6 /M /PE SUPPLY SPOOL [MOL DER PULLERTT'ER (UR/N6 Ul/E/V BAY/N6 Ol/EN INVENTORS W/AL/AM J. FERA/A/V mum/u J.#5255?" BY RLE 1. $H08ER7'1Z A 7'TOR/VEX5.

United States Patent 3,257,709 METHOD AND APPARATUS FOR MAKING ASTRllgJG 0F MOLDED ELECTRICAL RESIS- TOR William .1. Fern-an, William I.Herbst, and Erle I. Shobert 11, St. Marys, Pa, assignors to StackpoleCarbon Company, St. Marys, Pa, a corporation of Pennsylvania Filed Oct.Q, 1962, Ser. No. 229,363 11 Claims. (l. 29-15562) This inventionrelates to the making of electrical resistors by molding them around theends of wire leads, and more particularly to the making of a continuousstring of such resistors.

It is among the objects of this invention to provide a method andapparatus for making molded electrical resistors rapidly in such amanner that they can be operated upon and handled in a continuous stringof indefinite length which can be fed into an automatic machine forconnecting the individual resistors into electric circuits.

In accordance with this invention a long wire is out near its front endto form in front of the out a wirelead. This lead and the long wire arefed forward to a predetermined position where their adjacent ends willbe spaced apart. A resist-or body then is molded around and between thespaced ends. Periodically, the foregoing steps are repeated to formadditional resistor" bodies, each connected to the preceding one by awire lead cut from the long wire. As the string of resistor bodiesleaves the machine they can be treated or operated upon in various waysand then wound in a coil for further treatment and handling.

The preferred embodiment of the invention is illustrated in theaccompanying drawings, in which FIG. 1 is a fragmentary side view of mymachine;

FIG. 2 is a view of the front of the machine;

FIG. 3 is a horizontal section taken on the line IIIIII of FIG 1;

FIG. 4 is a fragmentary vertical section taken on the line IVIV of FIG.1;

FIGS. 5 to 9 are fragmentary vertical sections showing differentpositions of the movable parts of the machine as astring of resistors isbeing formed; and

FIG. is a diagram. of various steps in making a string of resistors inaccordance with my invention.

Referring to FIGS. 1 to 4 of the drawings, mounted in the bed 1 of amachine are four vertical posts 2 arranged in a rectangle, with theirupper ends mounted in the head 3 of the machine. Slidably mounted on thelower portions of the posts is a lower ram 4, from the center of which abottom punch 5 extends upward. Slidably mounted on the upper portions ofthe posts is an upper ram 6 that carries a downwardly extending toppunch 7 in line with the lower one. The two rams can be moved up anddown the posts by rods 8 that may be actuated in any suitable manner,such as by pistons and cylinders, cams or levers.

Between the two rams, a pair of dies 10 and 11 are slidably mounted onthe posts. They may be moved up and down independently of the punches bymeans of rods 12 actuated in any suitable manner. The two dies areprovided at their centers with aligned rectangular passages 13 and 14,each adapted to snugly receive the adjoining punch. When the dies areclosed, the two passage-s form a molding cavity. The lower punch may bepermanently disposed in the lower passage, but the upper punch is abovethe upper passage part of the time. The adjacent ends of the punches areconcave, as shown in FIG. 4, and when they are together in the center ofthe molding cavity they form a cylindrical chamber having the size ofthe resistor that is to be formed.

3,2517% Patented June 28, 1966 "ice The bottom of the upper die 10 infront of and behind its vertical passage 13 is provided with a pair ofaligned grooves 16 that are semicircular in cross section and of a sizeto fit half way around the wire that is fed to this 7 machine to formresistor leads. The grooves are midway between the opposite sides of.passage 13. Another pair of like grooves 17 is provided in the upperface of the lower die in positions to register with the upper grooveswhen the dies are closed. Each die also is provided with two verticalslots 18, one directly in front of and one behind its vertical passage.The upper and lower slots are aligned. Slidably mounted in the two lowerpassages are wire guides 19, the lower ends of which are secured to thelower ram 4. The upper portion of each guide projects above the lowerdie and is forked to provide a V notch :20, the lower end of which opensinto a narrow vertical slot 21 in the longitudinal vertical plane ofgrooves 16 and 17. The slot is about the same width as the grooves. Whenthe guides are in their upper positions, a wire lying in the grooveswill extend through slots 21.

Rigidly mounted at the back of the machine is a guide block 23, which isprovided with a bore 24 through it in line with the bore formed by thedie grooves when the dies are closed. This block receives the front endportion of a long flexible wire 25, from which resistor leads are to becut. The wire comes from a supply spool shown only in FIG. 10. The blockhas .a vertical passage 26 through it that intersects bore 24. Slidablymounted in this passage is a cutter blade 27, the lower end of whichnormally is above the bore. The blade may be moved down through thepassage in any suitable manner, preferably by being rigidly connected byan arm 28 to the upper ram so that they will move in unison.

The wire is fed from the supply spool forward through guide block 23 bya reciprocating feeder behind guide block 23. As shown in FIG. 5, thefeeder may take the form of a slide 30 mounted on a suitable support 31.The slide may be reciprocated toward and away from the block by anysuitable means. There is a vertical longitudinal slot 32 in the slide,through which the wire extends. Disposed in the end of this slot closestto the guide block is a gripper cam 33 pivotally suspended from a pin 34mounted in the slide. The shape of the cam is such that when the slideis moved forward toward the guide block the lower end of the cam willclamp the wire tightly against the bottom of the slot and thereby feedthe wire ahead at distance equal to the length of the stroke.

To charge the molding cavity with resistor-making material M (FIG. 7),such as a mixture of powdered graphite and a thermosetting resin, acharging plate 35 beneath upper punch '7 is slidably mounted on top ofthe upper die between guides 36 secured to that die. The plate can bemoved back and forth across the die at right angles to the wire grooves16 and 17 by any suitable means, such as by a rod 37 connected to apiston or other actuating means. The charging plate has a verticalopening 38 through it of about the same size and shape as the top of themolding cavity. The opening is large enough to permit the upper punch tomove down through the plate when the opening is directly over themolding cavity. At other times, opening 38 is located directly beneaththe outlet of a hopper 39 supported by the upper die. The hoppercontains the powdered material.

In operation, while the dies and punches and guides are retracted asshown in FIGS. 1 and 5, the long wire 25 extending through the feederslide 30 and into guide block 23 is advanced by the feeder until thefront end of the wire projects a short distance into the space betweenthe two vertical die passages 13 and 14. Assuming that a short lead wire41 is held between the dies at the opposite side of those passages, withits rear end projecting a short distance into the space between them,the upper die is lowered to engage the two wiresas shown in FIG. 6. Atthe same time, the bottom ram 4 is raised part way to lift wire guides19 in order to center the wires and make sure that they lie in ordirectly below grooves 16 in the upper die. The lower die then is raiseduntil it engages the upper one and the wires are enclosed by the twosets of grooves as shown in FIG. 7, whereby the mold cavity iscompleted. The lower ram is raised further at the same time. Thencharging plate 35 is moved to transfer a charge of resistor-makingmaterial M from hopper 39 to the mold cavity, into which the materialeither falls or is pushed by the upper punch when that punch is lowered.The two punches are moved toward each other in the mold cavity to moldthe material into a cylindrical resistor body 42 around the ends of thewires projecting into the cavity, as shown in FIG. 8. Preferably, at thesame time cutter blade 27 is moved down through the guide block to cutout a section of the wire at that point. The dies are then separated, asshown in FIG. 9, followed by the punches, and then the resistor body andthe long wire are moved ahead to locate the rear end of the rear leadnear the outlet side of the opened mold cavity and to locate the frontend of the long wire between the punches at the inlet side of thecavity. The cycle then is repeated, whereby a string of resistor bodiesis formed of any desired length. If the long wire is cut by a thinblade, the string will have to be advanced faster than the long wire inorder to space the rear end of the rear lead wire from the front end ofthe long wire at the mold cavity, so it is preferred to use the thickblade 27 so that the long wire and the string can move forward at thesame speed.

The successive resistor bodies and thin connecting leads are moved aheadperiodically by a puller formed from a reciprocating slide 44 on asupport 45 at the front of the machine. This slide likewise has avertical longitudinal slot 46 through it, but the slot is wide enough toreceive the resistor bodies. The base portion of the slide at the bottomof the slot is short and is inclined downwardly at its opposite ends topermit it to slide backward under each successive resistor body. Eachsuccessive wire lead is clamped against the base of the slot by agripper cam 47 suspended from a pivot pin 48 extended across the upperpart of the slot. The feeder and puller may operate in unison. Thearrows in FIGS. 5 and 7 show that they are in motion in the directionsindicated. In FIGS. 6, 8 and 9 the feeder and puller are stationary.

While a resistor body is still in the mold cavity, it is heatedsufficiently to partly cure it so that it will retain its shape and havesome strength until it can be completely cured later. The heating may bedone by electric heating elements 50 (FIGS. 5 to 9) mounted in chambers51 in the dies beside vertical passages 13 and 14.

It is desirable to paint the ends of the wire leads with carbon paintbefore the resistor bodies are molded around them, whereby to formbetter electrical connections between the leads and bodies. As shown inFIG. 10, the painting can be done by applying the paint to the long wire25 along short sections about as long as the resistor bodies and spacedapart about the same distance as those bodies. Each successive paintedsection travels through a dryer and then enters the feeder. When itreaches the guide block the central portion of the painted section iscut out by the cutter blade, leaving the adjacent ends of the wirespainted.

After the resistor bodies leave the puller they pass through a curingoven and then may travel through apparatus where the resistors areinsulated and color coded. Finally, the string of resistors is wound ina coil on a reel, which then may be immersed in a tank to impregnate theresistors with moisture-resisting material. After that, the coil isplaced in an oven to bake the resistors.

As the resistor string is uncoiled for use, the resistors may beseparated by cutting each successive wire lead in half by any suitablemeans.

It will be seen that by this invention resistors can be made rapidly andtreated and handled as a string of any desired length. The ability towind the string on a reel greatly facilitates the storage, shipping,handling and use of these resistors.

According to the provisions of the patent statutes, I have explained theprinciple of my invention and have illustrated and described what I nowconsider to represent its best embodiment. However, I desire to have itunderstood that, within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically illustrated anddescribed.

We claim:

1. In the making of a string of electrical resistors in which axiallyspaced resistor bodies are connected by wire leads, the methodcomprising cutting a long wire near its front end to form in front ofthe cut a wire lead, feeding said lead and long wire forward to apredetermined position where their adjacent ends will be spaced apart,pressure molding a resistor body around and between said spaced ends,and periodically repeating the foregoing steps to form additionalresistor bodies each connected to the preceding one by a wire lead cutfrom said long wire.

2. In the making of a string of electrical resistors in which axiallyspaced resistor bodies are connected by wire leads, the methodcomprising cutting a long wire near its front end to form in front ofthe cut a wire lead, feeding said lead and long wire forward to apredetermined position where their adjacent ends will be spaced apart,pressure molding around and between said spaced ends a resistor bodycontaining a thermo-setting resin and simultaneously heating said bodysufiiciently to retain its shape until said resin can be completelycured later, and periodically repeating the foregoing steps to formadditional resistor bodies each connected to the preceding one by a wirelead cut from said long wire and ready to be cured.

3. In the making of a string of electrical resistors in which axiallyspaced resistor bodies are connected by wire leads, the methodcomprising cutting a long'wire near its front end to form in front ofthe cut a wire lead, feeding said lead and long wire forward to apredetermined position where their adjacent ends will be spaced apart,pressure molding around and between said spaced ends a resistor bodycontaining a thermo-setting resin, periodically repeating the foregoingsteps to form a string of resistor bodies, intermittently moving saidstring ahead, and curing, insulating and color coding each successiveresistor body in the string.

4. In the making of a string of electrical resistors in which axiallyspaced resistor bodies are connected by wire leads, the methodcomprising cutting a long wire near its front end to form in front ofthe cut a wire lead, feeding said lead and long wire forward to apredetermined position where their adjacent ends will be spaced apart,pressure molding a resistor body around and between said spaced ends,periodically repeating the foregoing steps to form a string of resistorbodies, winding said string onto a reel, and impregnating the resistorbodies on the reel with moisture-resisting material.

5. In the making of a string of electrical resistors in which axiallyspaced resistor bodies are connected by wire leads, the methodcomprising cutting a section from a long wire near its front end to formin front of the cut a wire lead, feeding said lead and long wire forwarda predetermined distance, then pressure molding a resistor body aroundand between the spaced wire ends produced by said cutting, andperiodically repeating the foregoing steps to form additional resistorbodies each connected to the preceding one .by a wire lead.

6. In the making of a string of electrical resistors in which axiallyspaced resistor bodies are connected by wire leads, the methodcomprising painting with carbon paint a short length of a long wire nearits front end, allowing the paint to dry, cutting a section of the wirefrom the middle of said .painted length to form in front of the cut awire lead having a painted end portion, feeding said lead and long wireforward a predetermined distance, then pressure molding a resistor bodyaround and between the spaced painted wire end portions produced by saidcutting, and periodically repeating the foregoing steps to formadditional resistor bodies each connected to the preceding one by a wirelead cut from said long wire.

7. In the making of a string of electrical resistors in which axiallyspaced resistor bodies are connected by wire leads, the methodcomprising cutting a section from a long wire near its front end to formin front of the cut a wire lead, feeding said lead and long wire forwardin unison a predetermined distance and then holding them stationary,pressure molding a resistor body of greater length than said sectionaround and between the spaced wire ends produced by said cutting, andperiodically repeating the foregoing steps to form additional resistorbodies each connected to the one in front of it by a wire lead out fromsaid long wire.

8. In the making of a string of electrical resistors in which axiallyspaced resistor bodies are connected by wire leads, the methodcomprising cutting a section from a long wire near its front end to formin front of the cut a wire lead, pulling said lead forward apredetermined distance, simultaneously pushing the long wire ahead apredetermined distance while maintaining it spaced from said lead, thenpressure molding a resistor body around and. between the spaced wireends produced by said cutting, and periodically repeating the foregoingsteps to form additional resistor bodies each connected to the one aheadof it by a wire lead cut from said long wire.

9. Apparatus for making a string of electrical resistors in whichaxially spaced resistor bodies are connected by flexible wire leads,comprising upper and lower dies, means for moving the dies into and outof engagement with each other, the dies being provided with a pair ofaligned vertical passages therethrough forming a molding cavity when thedies are closed, a vertically reciprocable bottom punch in the lowerpassage, a vertically reciprocable top punch normally disposed above theupper passage, the closed dies being formed to hold between them at thefront and back of said cavity and in axial alignment a short wire leadand the front end portion of a long flexible wire with the adjacent endsthereof projecting into the cavity but spaced apart, means fordelivering a charge of powdered resistor material to the top of themolding cavity, means for moving said punches toward and away from eachother in said cavity to mold said material into a re sistor body withsaid wire ends embedded therein, cutting means behind the dies adaptedto cut said long Wire to form a second short wire lead projecting fromsaid body, means for pulling said resistor body forward away from themolding cavity when the dies and punches are retracted until the freeend of said second lead will project only a short distance into thecavity, and means for feeding the long wire-forward between theretracted dies until its front end will project only a short distanceinto said cavity, whereby when the dies are closed again the moldingcavity will be ready to receive another charge of powdered resistormaterial.

10. Apparatus according to claim 9, in which said cutting means includesa member provided with a wire-receiving longitudinal bore therethroughfor guiding the wire to the dies, said member having a transversepassage therethrough intersecting said bore, and a cutting bladedisposed in said transverse passage normally at one side of thelongitudinal bore and movable across it to cut a section from a wire inthe bore.

11. Apparatus as recited in claim 9, in which said dies are providedwith vertically aligned slots at the front and back of said verticalpassages, and a pair of vertically reciprocable wire guides are mountedin said slots in the lower die, each guide being provided With adownwardly extending V notch terminating at its lower end in a verticalslit for receiving a wire when the guides are moved up in the upperslots.

References Cited by the Examiner UNITED STATES PATENTS 2,500,258 4/1950Mazzoni l8-36 2,577,584 12/1951 Hofreiter 18--16 2,608,633 8/1952 Bol201-63 2,669,770 2/1954 Brewer 29155.5 2,885,524 5/1959 Eisler 29155.622,924,850 2/ 1960 Schultz 1836 3,083,445 4/1963 Hill 29155.62 3,110,08811/1963 Blom 29-1555 JOHN F. CAMPBELL, Primary Examiner.

r 1W. BOCK, I. M. ROMANCHIK, IR.,

Assistant Examiners.

1. IN THE MAKING OF A STRING OF ELECTRICAL RESISTORS IN WHICH AXIALLYSPACED RESISTOR BODIES ARE CONNECTED BY WIRE LEADS, THE METHODCOMPRISING CUTTING A LONG WIRE NEAR ITS FRONT END TO FORM IN FRONT OFTHE CUT A WIRE LEAD, FEEDING SAID LEAD AND LONG WIRE FORWARD TO APREDETERMINED POSITION WHERE THEIR ADJACENT ENS WILL BE SPACED APART,PRESSURE MOLDING A RESISTOIR BODY AROUND AND BETWEEN SAID SPACED ENDS,AND PERIODICALLY REPEATING THE FOREGOING STEPS TO FORM ADDITIONALRESISTOR BODIES EACH CONNECTED TO THE PRECEDIONG ONE BY A WIRE LEAD CUTFROM SAID LONG WIRE.
 9. APPARATUS FOR MAKING A STRING OF ELECTRICALRESISTORS IN WHICH AXIALLY SPACED RESISTOR BODIES ARE CONNECTED BYFLEXIBLE WIRE LEADS, COMPRISING UPPER AND LOWER DIES, MANS FOR MOVINGTHE DIES INTO AND OUT OF ENGAGEMENT WITH EACH OTHER, THE DIES BEINGPROVIDED WITH A PAIR OF ALIGNED VERTICAL PASSAGES THERETHROUGH FORMING AMOLDING CAVITY WHEN THE DIES ARE CLOSED, A VERTICALLY RECIPROCABLEBOTTOM PUNCH IN THE LOWER PASSAGE, A VERTICALLY RECIPROCABLE TOP PUNCHNORMALLY DISPOSED ABOVE THE UPPER PASSAGE, THE CLOSED DIES BEING FORMEDTO HOLD BETWEEN THEM AT THE FRONT AND BACK OF SAID CAVITY AND IN AXIALALIGNMENT A SHOT WIRE LEAD AND THE FRONT END PORTION OF A LONG FLEXIBLEWIRE WITH THE ADJACENT ENDS THEREOF PROJECTING INTO THE CAVITY BUTSPACED APART, MEANS FOR DELIVERING A CHARGE OF POWDERED RESISTORMATERIAL TO THE TOP OF THE MOLDING CAVITY, MEANS FOR MOVING SAID PUNCHESTOWARD AND AWAY FROM EACH OTHER IN SAID CAVITY TO MOLD SAID MATERIALINTO A RESISTOR BODY WITH SAID WIRES ENDS EMBEDDED THEREIN, CUTTINGMEANS BEHIND THE DIES ADAPTED TO CUT SAID LONG WIRE TO FORM A SECONDSHORT WIRE LEAD PROJECTIONG FROM SAID BODY MEANS FOR PULLING SAIDRESISTOR BODY FORWARD AWAY FROM THE MOLDING CAVITY WHEN THE DIES ANDPUNCHES ARE RETRACTED UNTIL THE FREE END OF SAID SECOND LEAD WILLPROJECT ONLY A SHORT DISTANCE INTO THE CAVITY, AND MEANS FOR FEEDING THELONG WIRE FORWARD BETWEEN THE RETRACTED DIES UNTIL ITS FRONT END WILLPROJECT ONLY A SHORT DISTANCE INTO SAID CAVITY, WHEREBY WHEN THE DIESARE CLOSED AGAIN THE MOLDING CAVITY WILL BE READY TO RECEIVE ANOTHERCHARGE OF POWDERED RESISTOR MATERIAL.